Tantalum Capacitors

[bitrex]

So I'm working on repairing a Korg MS2000B synthesizer for a friend with
a dead power supply. Here's the service manual:

http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf

The first thing I notice when looking inside is that the small SMT 100uF
10V tantalum capacitor C109 has completely vacated - it appears to be
gone, blown right off the board. There are some little fragments
rattling around in the case.

I have little experience with tantalum capacitors. Any suggestions for
a more reliable replacement?

[Tom Miller]

"bitrex" <bit...@de.lete.earthlink.net> wrote in message
news:5601ad59$0$5917$4c5e...@frugalusenet.com...

Use 2.5 times the applied voltage or more.

Or use an aluminum electrolytic 2 - 3 times capacitance.

[Jeff Liebermann]

I don't think there's a reliability issue here. C109 (located on the
Power / MIDI board schematic, is the initial output filter capacitor
in a 3.3V switching power supply. There are other 100 uf caps
surrounding it, but it seems to be the only tantalum cap, which
suggests that the designer needed some specific characteristic of the
cap to make things work. Methinks a change of capacitor type might
not be such a great idea.

What would make the cap explode? My guess(tm) is that someone plugged
in a wrong voltage power supply, which blew up FET (F1) which then
applied overvoltage to the tantalum. It much have been quite a large
jolt as tantalums using produce a low resistance "short" which then
gets hot and starts smoking toxic fumes. I would look around for
other parts in the power supply section that may be been destroyed,
such as the other caps along the 3.3V rail.

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[bitrex]

I notice now that there seems to be some very light heat discoloration
around the common mode choke L10-L11-L12.

I don't see anything immediately wrong with F1 and it passes the "smell
test" so I dunno.

[John Larkin]

On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

Dry-slug tantalums across power rails are bad news. High dV/dT
literally ignites them; MnO2 is the oxidizer and tantalum is the fuel.

Derate them 3:1 on voltage, or use something else. Polymer aluminums
are good, and some come in a tantalum-like surface mount package.

[Syd Rumpo]

+1

Cheers
--
Syd

[bitrex]

Is there anything I can use temporarily in its place, that I might have
in stock, to try and get that switcher up and running while I wait for
the appropriate part?

[John Larkin]

On Tue, 22 Sep 2015 20:22:49 -0400, bitrex
<bit...@de.lete.earthlink.net> wrote:

>On 9/22/2015 4:40 PM, John Larkin wrote:
>> On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann <je...@cruzio.com>
>> wrote:
>>
>>> On Tue, 22 Sep 2015 15:34:51 -0400, bitrex
>>> <bit...@de.lete.earthlink.net> wrote:
>>>
>>>> So I'm working on repairing a Korg MS2000B synthesizer for a friend with
>>>> a dead power supply. Here's the service manual:
>>>>
>>>> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf

What a horrible schematic! A mosfet is "F1" and a fuse is "FU1" !
Connector names are all over the place. And worse.

Replace C109 with most any 100 uF cap.

What's with the 21 resistors between AGND and DGND? That's crazy.

[Jeff Liebermann]

On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin
<jjla...@highlandtechnology.com> wrote:

>Dry-slug tantalums across power rails are bad news. High dV/dT
>literally ignites them; MnO2 is the oxidizer and tantalum is the fuel.

That's what I've read everywhere. Yet, I spent 10 years shipping
marine radios that were literally crammed with dipped and molded
tantalum caps on power supply rails with never a problem. The only
ones I've ever seen go up in smoke were reverse polarized (which
produced an impressive red glowing piece of slag and plenty of white
smog). Mostly, these caps were 25V caps on the 12V (nominal) power
supply lines and 16V caps on the 8 and 10V regulated lines. There
were also a bunch used in audio circuits.

However, we never used tantalums on the output of a switcher, where I
would expect problems. I guess using a tantalum in this 3.3V switcher
would qualify. However, at the time (1970's) the literature declared
that high voltage spikes were the culprit, not voltage slew rate.
Since these often appear together, I can see where there might be some
confusion.

>Derate them 3:1 on voltage, or use something else. Polymer aluminums
>are good, and some come in a tantalum-like surface mount package.

The original cap is a 100uF 10v tantalum which is already 3:1 derated
in a 3.3 VDC power supply. However, that doesn't included voltage
spikes from the nearby inductor.

Judging by the age of the Korg, I would guess(tm) axial leads not SMT.
100uf 10-16V From Digikey:
<http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69=80&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25>
For fast delivery, there's probably something on eBay:
<http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf>

[bitrex]

Nope, the power supply is almost all SMT, including the tantalum. The
only through hole parts is the switcher inductor and the other large
capacitors, which are a mix of organic polymer and regular electrolytic.

[bitrex]

On 9/22/2015 8:55 PM, Jeff Liebermann wrote:

This thing cost an arm and a leg when it was new 15 years ago. Inside
the very large case there actually isn't very much - there's a board
which holds all the front panel controls, and everything else including
the power supply and output jacks are on a single mainboard measuring
maybe 8"x10".

[Jeff Liebermann]

On Tue, 22 Sep 2015 21:23:47 -0400, bitrex
<bit...@de.lete.earthlink.net> wrote:

>> Judging by the age of the Korg, I would guess(tm) axial leads not SMT.
>> 100uf 10-16V From Digikey:
>> <http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69=80&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25>
>> For fast delivery, there's probably something on eBay:
>> <http://www.ebay.com/sch/i.html?_nkw=polymer+capacitor+100uf>

>Nope, the power supply is almost all SMT, including the tantalum. The
>only through hole parts is the switcher inductor and the other large
>capacitors, which are a mix of organic polymer and regular electrolytic.

Bad guess(tm). Sorry. I couldn't tell from the "manual" because none
of the caps are listed in the parts list.

This should work for SMT on Digikey:
<http://www.digikey.com/product-search/en?pv13=67&pv63=19&pv63=11&pv63=449&pv63=489&pv69=3&FV=fff40002%2Cfff80532&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25>
The eBay link includes both through-hole and SMT.

[John Larkin]

On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin
><jjla...@highlandtechnology.com> wrote:
>
>>Dry-slug tantalums across power rails are bad news. High dV/dT
>>literally ignites them; MnO2 is the oxidizer and tantalum is the fuel.
>
>That's what I've read everywhere. Yet, I spent 10 years shipping
>marine radios that were literally crammed with dipped and molded
>tantalum caps on power supply rails with never a problem. The only
>ones I've ever seen go up in smoke were reverse polarized (which
>produced an impressive red glowing piece of slag and plenty of white
>smog). Mostly, these caps were 25V caps on the 12V (nominal) power
>supply lines and 16V caps on the 8 and 10V regulated lines. There
>were also a bunch used in audio circuits.

The tantalum thing is very erratic. Some batches blow up, some are
fine.

>
>However, we never used tantalums on the output of a switcher, where I
>would expect problems. I guess using a tantalum in this 3.3V switcher
>would qualify. However, at the time (1970's) the literature declared
>that high voltage spikes were the culprit, not voltage slew rate.
>Since these often appear together, I can see where there might be some
>confusion.

I know for sure that tantalums sometimes blow up at below their rated
voltages, with no overshoot spikes. It's dV/dT, namely peak current,
that can ignite tiny particles of tantalum, which then burn in the
solid MnO2 electrolyte.

>
>>Derate them 3:1 on voltage, or use something else. Polymer aluminums
>>are good, and some come in a tantalum-like surface mount package.
>
>The original cap is a 100uF 10v tantalum which is already 3:1 derated
>in a 3.3 VDC power supply. However, that doesn't included voltage
>spikes from the nearby inductor.

Could be. Or maybe there was a lot of dV/dT. Or maybe some other
failure mechanism.

Tantalums are just right for some things, but have to be used
carefully.

https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Bang.jpg

https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Fried_Tant_1.JPG

[joe hey]

On Tue, 22 Sep 2015 17:55:51 -0700, Jeff Liebermann wrote:

> On Tue, 22 Sep 2015 13:40:36 -0700, John Larkin
> <jjla...@highlandtechnology.com> wrote:
>
>>Dry-slug tantalums across power rails are bad news. High dV/dT literally
>>ignites them; MnO2 is the oxidizer and tantalum is the fuel.
>
> That's what I've read everywhere. Yet, I spent 10 years shipping marine
> radios that were literally crammed with dipped and molded tantalum caps
> on power supply rails with never a problem. The only ones I've ever
> seen go up in smoke were reverse polarized (which produced an impressive
> red glowing piece of slag and plenty of white smog). Mostly, these caps
> were 25V caps on the 12V (nominal) power supply lines and 16V caps on
> the 8 and 10V regulated lines. There were also a bunch used in audio
> circuits.
>
> However, we never used tantalums on the output of a switcher, where I
> would expect problems. I guess using a tantalum in this 3.3V switcher
> would qualify. However, at the time (1970's) the literature declared
> that high voltage spikes were the culprit, not voltage slew rate.
> Since these often appear together, I can see where there might be some
> confusion.

Tantalums have such a low HF resistance that it is sometimes recommended
to put a current limiting resistor in series if there is a serious ripple
voltage around. I've witnessed a lot of IGBT's being blown up because
those resistors were failing. The voltage feeding the tantalums had such
a large HF ripple due to the switching of the IGBT's that it blew the
tantalums out of the control board, after which the IGBT's also went to
pieces.

joe

[joe hey]

That's why in those cases a series resistor might be recommended in order
to limit the current spikes.

joe

[mrob...@att.net]

In sci.electronics.repair John Larkin <jjla...@highlandtechnology.com> wrote:
>>>> On Tue, 22 Sep 2015 15:34:51 -0400, bitrex
>>>> <bit...@de.lete.earthlink.net> wrote:
>>>>

>>>>> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf

>
> What's with the 21 resistors between AGND and DGND? That's crazy.

They're all marked "NU", which seems to mean Not Used. Other parts of
that sheet have "NU" resistors in similar nonsensical places, like
across the fuse or across the power switch. I suspect there are places
for all of these resistors on the board, but they don't populate them at
the factory except for test.

Matt Roberds

[rickman]

Add series resistance to a tantalum cap and you have just created an
electrolytic replacement.

--

Rick

[Trevor Wilson]

**Tants are not unreliable. In fact, IME, they're more reliable than
aluminium electros (not a scientific study though - just seat of the
pants). They do not tolerate reverse Voltages particularly well though.

Use another tantalum. Solid are best, but hard to find.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[joe hey]

Sorry, I forgot to mention to put the resistance in between the power
line and the tantalum.

joe

[Phil Hobbs]

Al polys can make voltage regulators oscillate. Tantalums have a nice
middle-of-the-road ESR that makes 7800s happy.

The ignition problem is quite real--see
<http://electrooptical.net/www/sed/TantalumCapReforming_25272-what_a_cap_astrophe.pdf>

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[John Larkin]

My favorite cheap "MDO" regulator, the LM1117, loves a 10 uF tantalum
on its output.

[John Larkin]

But than it doesn't bypass the power rail!

[John Larkin]

On Wed, 23 Sep 2015 16:01:26 +1000, Trevor Wilson
<tre...@SPAMBLOCKrageaudio.com.au> wrote:

>On 23/09/2015 5:34 AM, bitrex wrote:
>> So I'm working on repairing a Korg MS2000B synthesizer for a friend with
>> a dead power supply. Here's the service manual:
>>
>> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf
>>
>> The first thing I notice when looking inside is that the small SMT 100uF
>> 10V tantalum capacitor C109 has completely vacated - it appears to be
>> gone, blown right off the board. There are some little fragments
>> rattling around in the case.
>>
>> I have little experience with tantalum capacitors. Any suggestions for
>> a more reliable replacement?
>
>**Tants are not unreliable. In fact, IME, they're more reliable than
>aluminium electros (not a scientific study though - just seat of the
>pants). They do not tolerate reverse Voltages particularly well though.
>
>Use another tantalum. Solid are best, but hard to find.

Most tantalum caps are solids, with the MnO2 electrolyte. Less common
are liquid types and polymers.

[Ralph Mowery]

<mrob...@att.net> wrote in message news:mtt9f3$96p$1...@dont-email.me...

That is somewhat of a crazy schematic. I bet some of the NU resistors
could be some 0 ohm resistors. They are mainly jumper wires made inside a
blob of material that resembles a resistor in size. They have been used to
be in inserted by machine to jump over places where a circuit trace can not
be made.

[joe hey]

No, we did it locally, every IC that was uncoupled with a tantalum, we
put a small resistor from the power rail to the tantalum and the problem
was solved. I clearly remember reading this advice in some tantalum's
datasheet or application note. As those IC's consume very little, the DC
voltage drop over the resistance was negligible, but the reduction in
current spikes through the tantalums was considerable.
They didn't blow up anymore and neither did the IGBTs.

joe

[Cydrome Leader]

Can somebody decode "postprocessing fixture" back into English? I have
idea what the author is talking about or what the "fix" really was.

[Phil Hobbs]

He ramped up the supply slowly with a current limit, to give the tants a
chance to clear the damage.

[rickman]

Is it about clearing damage or just to show the added resistance
prevented the failure? I found the story a bit hard to follow.

--

Rick

[krw]

The point being that by adding the resistor, you've increased the
"ESR" of the cap(-resistor). You might just as well use an aluminum
cap in its place if ESR doesn't matter.

[John Devereux]

No there is still a low-ESR decoupling for the IC. I do that a lot since
it isolates the IC rail from spikes on the main power rail. (Not with
tants though).


--

John Devereux

[rickman]

He is talking about this...

Vcc ---/\/\/\---+-------+
| |
IC =
| |
--- ---
- -
Not this...

Vcc ----+----/\/\/\-----+
| |
IC =
| |
--- ---
- -

--

Rick

[Jeff Liebermann]

On 23 Sep 2015 04:18:36 GMT, joe hey <joe...@mailinator.com> wrote:

>Tantalums have such a low HF resistance that it is sometimes recommended
>to put a current limiting resistor in series if there is a serious ripple
>voltage around.

Really?
<http://my.execpc.com/~endlr/esr.html>
Click on the graph near the bottom of the page. Note that the low-ESR
aluminum electrolytic is only slightly worse than the equivalent
tantalum. If polymer caps were added to the graph, it would be about
the same as tantalum.

The reason we used tantalum (in marine radios) over electrolytics was
that they were smaller, lasted longer, were sealed, more stable
capacitance over temperature, more stable ESR over temperature, and
were easier to handle in a wave solder and washing machine
environment. While each benefit for tantalum is admittedly minor, the
combination of all the aforementioned benefits made them quite a
superior device. The only downside was the cost, which limited their
use to areas where a very low ESR was needed.

Your "current limiting resistor" sounds like something that would
raise the ESR of the device by the resistor value. Much depends on
the ripple current, which presumably in a switching power supply
filter cap, is quite high.

When playing with ESR's of less than 1 ohm, minor variables such as
PCB plating thickness and trace width/length become significant. When
the lowest ESR is at the series self resonant frequency of the
capacitor, the selection of type, value, voltage, package, etc also
become important. Much of the RF circuitry involved in a radio
requires broadband bypassing. That rapidly becomes an exercise in
capacitor selection based on series resonant frequencies and lowest
overall ESR. It was not unusual to have 3 different bypass caps in
parallel at key locations, such as the corners of PCB's to chassis
ground points. Adding a series resistor to the tantalum cap would not
have worked for obtaining the lowest possible ESR.

>I've witnessed a lot of IGBT's being blown up because
>those resistors were failing. The voltage feeding the tantalums had such
>a large HF ripple due to the switching of the IGBT's that it blew the
>tantalums out of the control board, after which the IGBT's also went to
>pieces.

Did the ripple voltage on the power supply line increase with the
added series resistance?

[Jeff Liebermann]

On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin
<jjla...@highlandtechnology.com> wrote:

>The tantalum thing is very erratic. Some batches blow up, some are
>fine.

I guess I should mention that Intech had two divisions. I worked for
the marine radio division. There was also a "modular products"
division that made military grade modules (A/D, D/A, amps, etc). Both
divisions shared many of the same components including a wide
selection of tantalum caps. Most of the modules ran on +15/-15 VDC
and used 35 VDC rated tantalums. As I vaguely recall, there were no
aluminum caps used in anything that had to work from -40C to +105C. If
tantalums were that failure prone, they would never have survived in a
mil spec environment.

Some typical radio boards. This is Intech M3600 2-30 MHz 150 watt PEP
synthesized SSB radio circa 1977(?):
<http://www.hellocq.net/forum/read.php?tid=226493>
The boards are a mix of purple potted electrolytics and blue or orange
colored tantalums. No failures in 10 years of similar radios.

There also seems to be an aging mechanism involved. I'm the not so
proud owner of several Wavetek 3000B service monitors:
<http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html>
Some of the tantalums have shorted over the years. I'm replacing them
as I blunder forward. No fires, smoke, or discoloration in about 10
years of fixing these. I also have some other equipment with similar
tantalum problems. I recently repaired an M3600 radio which showed no
evidence of deteriorating or failed tantalums. Has something changed
in the last 40 years in how tantalums are made?

>I know for sure that tantalums sometimes blow up at below their rated
>voltages, with no overshoot spikes. It's dV/dT, namely peak current,
>that can ignite tiny particles of tantalum, which then burn in the
>solid MnO2 electrolyte.

I think you mean dI/dT which provides the heating necessary to ignite
the tantalum. That all sounds logical, but doesn't explain why a
similar amount of heating caused by normal ripple current doesn't set
fire to the capacitor. I've seen some heat darkened tantalums
operating normally without ignition. Like the bulging electrolytics
and burning LiIon batteries, I suspect there's been some changes in
production methods (like skipping important steps to save pennies).

>>The original cap is a 100uF 10v tantalum which is already 3:1 derated
>>in a 3.3 VDC power supply. However, that doesn't included voltage
>>spikes from the nearby inductor.

>Could be. Or maybe there was a lot of dV/dT. Or maybe some other
>failure mechanism.
>
>Tantalums are just right for some things, but have to be used
>carefully.
>https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Bang.jpg
>https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Fried_Tant_1.JPG

Nice photos. Having done post mortem failure analysis a few times, I
like to look at the damage and try to guess what was the cause. It's
fairly easy to inspect the remains and estimate the violence of the
failure. For tantalum, there's usually something left of the wire
leads or carbonized slug. It gets hot, belches flames, carbonizes,
falls apart, which finally breaks the connection.

However, the OP mentioned that:

"The first thing I notice when looking inside is that the small
SMT 100uF 10V tantalum capacitor C109 has completely vacated -
it appears to be gone, blown right off the board. There are
some little fragments rattling around in the case."

That's not what I consider to be a conventional tantalum burn failure.
The cap should have looked like the one in the above photos. Something
caused this one to explode rather than burn, which is why I suggested
that a much higher voltage wall wart was involved. I don't think the
tantalum was at fault simply because it was the first thing to blow
and was the most obvious physical failure.

[Phil Hobbs]

An aluminum electro in parallel with a smaller ceramic makes a nice
lead-lag network for the voltage regulator, if you do it right.

[John Larkin]

One thing that doesn't show up on the power supply schematic sheet is
the zillions of chip bypass caps on other sheets. One might have tens
of uF of paralleled super-low ESR ceramic caps on a big power pour.

A tantalum seems to have the right ESR to damp the whole mess, even
when a regulator should be unstable with just the ceramics.

One test for stability is to apply a pulse load and see how the
regulator reacts.

I saw one big board (part of an Anritsu DRAM tester system) that had
3000 bypass caps. It's not unusual to see an FPGA appnote that
recommends a hundred caps or so per chip.

[Phil Hobbs]

Wet tants are super-expensive. ISTR they're basically military-only.

[John Larkin]

On Wed, 23 Sep 2015 16:15:59 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>On 09/23/2015 10:24 AM, John Larkin wrote:
>> On Wed, 23 Sep 2015 16:01:26 +1000, Trevor Wilson
>> <tre...@SPAMBLOCKrageaudio.com.au> wrote:
>>
>>> On 23/09/2015 5:34 AM, bitrex wrote:
>>>> So I'm working on repairing a Korg MS2000B synthesizer for a friend with
>>>> a dead power supply. Here's the service manual:
>>>>
>>>> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf
>>>>
>>>> The first thing I notice when looking inside is that the small SMT 100uF
>>>> 10V tantalum capacitor C109 has completely vacated - it appears to be
>>>> gone, blown right off the board. There are some little fragments
>>>> rattling around in the case.
>>>>
>>>> I have little experience with tantalum capacitors. Any suggestions for
>>>> a more reliable replacement?
>>>
>>> **Tants are not unreliable. In fact, IME, they're more reliable than
>>> aluminium electros (not a scientific study though - just seat of the
>>> pants). They do not tolerate reverse Voltages particularly well though.
>>>
>>> Use another tantalum. Solid are best, but hard to find.
>>
>> Most tantalum caps are solids, with the MnO2 electrolyte. Less common
>> are liquid types and polymers.
>>
>>
>Wet tants are super-expensive. ISTR they're basically military-only.
>
>Cheers
>
>Phil Hobbs

Pretty much. We used to use them in mil systems. The cases were
silver, back when silver wasn't too expensive. The electrolyte is
acid, which eventually eats its way out. I think the cases may be
tantalum now.

CSR13 part numbers, something like that. A few bucks each, about the
price of a low-end steak dinner then.

[piglet]

On 23/09/2015 15:24, John Larkin wrote:
> Most tantalum caps are solids, with the MnO2 electrolyte. Less common
> are liquid types and polymers.
>

There is even solid aluminum, now only made by Vishay (I think) and cost
more than equivalent tantalum. The ones I use are resin dipped through
hole parts and look like a big resin dipped tantalum bead. Nice caps,
very low ESR and supposedly very reliable, claim "no-known wear-out
mechanism".

piglet

[John Larkin]

On Wed, 23 Sep 2015 21:34:38 +0100, piglet <erichp...@hotmail.com>
wrote:

Do you mean polymer aluminums? Those are great, super low ESR. We use
United Chem-Com and Nichicon. 47 cents for 180 uF 6.3 volts, about 2x
tha price of a regular aluminum cap.

[piglet]

No, I don't think these are polymer, may even predate polymer
electrolyte. Uses Mn02 I think like solid Ta. See Vishay SAL 122 series.
Temp range -55 to +175 C.

piglet

[joe hey]

Look at it like this (you might switch to fixed width font).
____
+ ---|____|-----------------
small |
R |tant
---
--- --> to IC Vcc/GND
|
|
- --------------------------

It's a filter now.
Still the same (or even better) ripple suppression.
(Almost) no lowering in supply voltage for the IC.
Tantalum as near as possible to the IC in order to take account of the EMC
induced voltages also, which are caused by the HF high current switching.

joe

[joe hey]

Right.
It was (at that time) even recommended.

joe

[joe hey]

Correct.

joe

[joe hey]

On Wed, 23 Sep 2015 11:58:43 -0700, Jeff Liebermann wrote:

> On Tue, 22 Sep 2015 19:02:33 -0700, John Larkin

}snip{

>>I know for sure that tantalums sometimes blow up at below their rated
>>voltages, with no overshoot spikes. It's dV/dT, namely peak current,
>>that can ignite tiny particles of tantalum, which then burn in the solid
>>MnO2 electrolyte.
>
> I think you mean dI/dT which provides the heating necessary to ignite
> the tantalum. That all sounds logical, but doesn't explain why a
> similar amount of heating caused by normal ripple current doesn't set
> fire to the capacitor. I've seen some heat darkened tantalums operating
> normally without ignition. Like the bulging electrolytics and burning
> LiIon batteries, I suspect there's been some changes in production
> methods (like skipping important steps to save pennies).

Are you sure? I understood that the I=C.dV/dt was responsible for the
damage. The higher dV/dt, the higher I. And the longer the dV/dt
continues, the hotter the C gets.

}snip{

joe

[joe hey]

On Wed, 23 Sep 2015 11:16:35 -0700, Jeff Liebermann wrote:

> On 23 Sep 2015 04:18:36 GMT, joe hey <joe...@mailinator.com> wrote:
>
>>Tantalums have such a low HF resistance that it is sometimes recommended
>>to put a current limiting resistor in series if there is a serious
>>ripple voltage around.
>
> Really?

Yes

}sorry for snipping, but I hate scrolling a lot{

> Your "current limiting resistor" sounds like something that would raise
> the ESR of the device by the resistor value. Much depends on the ripple
> current, which presumably in a switching power supply filter cap, is
> quite high.

If you read the post carefully, you'd see that between power supply and C
there is a small R, which gives a tiny reduction of voltage to the IC,
and then there is the C // Vcc-GND. So the IC sees the same (or even
smaller) ripple from the power supply, EMC suppression is still the same
(or even better due to more damping of the ringing) and everything went
fine from then on.

> When playing with ESR's of less than 1 ohm, minor variables such as PCB
> plating thickness and trace width/length become significant. When the
> lowest ESR is at the series self resonant frequency of the capacitor,
> the selection of type, value, voltage, package, etc also become
> important.

Yes. And all those factors are uncertain to a high degree.
Therefore it could be advisable to just add a resistor of a known value,
if your design permits it.

> Much of the RF circuitry involved in a radio requires
> broadband bypassing. That rapidly becomes an exercise in capacitor
> selection based on series resonant frequencies and lowest overall ESR.
> It was not unusual to have 3 different bypass caps in parallel at key
> locations, such as the corners of PCB's to chassis ground points.
> Adding a series resistor to the tantalum cap would not have worked for
> obtaining the lowest possible ESR.

Indeed, not in that case. But where we had the problem, it worked well.

>>I've witnessed a lot of IGBT's being blown up because those resistors
>>were failing. The voltage feeding the tantalums had such a large HF
>>ripple due to the switching of the IGBT's that it blew the tantalums out
>>of the control board, after which the IGBT's also went to pieces.

Indeed.

> Did the ripple voltage on the power supply line increase with the added
> series resistance?

After finding out the problem, we (finally) read up to the specs and
recommendations, found the suggestion to add small R's, did it, and the
problem was gone. We did not measure ripple voltage. I guess that would
have been useless because the problem was caused by EMC, and the
measuring probe would probably have suffered the same problem and not
given the right picture.

joe

[krw]

On Wed, 23 Sep 2015 18:35:02 +0100, John Devereux

No, the point is that there is no reason to use a tantalum cap if
you're going to blow its ESR with a resistor. Just use an aluminum.

[krw]

Nevermind!

I sit corrected. ;-)

[Ralph Mowery]

"krw" <k...@nowhere.com> wrote in message >

> No, the point is that there is no reason to use a tantalum cap if
> you're going to blow its ESR with a resistor. Just use an aluminum.

I was thinking one reason to use the tantalum was because it could pack more
capacitance in a smaller space.

[JW]

On Wed, 23 Sep 2015 22:17:58 +0100 piglet <erichp...@hotmail.com> wrote
in Message id: <mtv4qh$o6i$1...@dont-email.me>:

Couldn't find anything on them. Do you mean SAL 128?
http://www.vishay.com/docs/28354/128salrpm.pdf
End of Life. Last Available Purchase Date is 30-December-2015

Must be too reliable. :)

[piglet]

Yes SAL128 are miniature, just a bit smaller than the 122 range. Shame
about the EOL - they are great parts and should have been much more
popular. The axial part (SAL123) is rated from -80 to +200 deg C.

Polymer can't match that temp range (yet).

piglet

[John Larkin]

On Thu, 24 Sep 2015 15:15:22 +0100, piglet <erichp...@hotmail.com>

Polymers are great cold, below 0C when wet aluminums freeze and ESR
skyrockets. I suppose the polymers melt at high temp.

The UCC parts are rated for -55 to 105C.

https://dl.dropboxusercontent.com/u/53724080/Parts/Caps/Polymer_ESR.JPG

[Chris Jones]

I suspect you need to see a diagram of the circuit because you are
thinking of a resistor directly in series with the capacitor whereas Joe
and John were thinking of placing the capacitor directly across the load
(chip) and a resistor between the regulator and the supply pin of the
load (chip), (with its capacitor).

The ESR would be high if measured from the location of the regulator,
because there would be a resistor between the regulator and the
capacitor. The ESR would appear low if measured from the location of the
chip which is the load (chip), because the capacitor is directly in
parallel with the load (chip). The disadvantage of this arrangement is
that the average (DC) load current flows through the resistor which
might cause an annoying reduction in the supply voltage at the load.

[Chris Jones]

Nevermind, others have already said what I tried to say.

[Jon Elson]

bitrex wrote:

> So I'm working on repairing a Korg MS2000B synthesizer for a friend with
> a dead power supply. Here's the service manual:
>
> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf
>
> The first thing I notice when looking inside is that the small SMT 100uF
> 10V tantalum capacitor C109 has completely vacated - it appears to be
> gone, blown right off the board. There are some little fragments
> rattling around in the case.
>
> I have little experience with tantalum capacitors. Any suggestions for
> a more reliable replacement?

One other option is Niobium Oxide caps, sold under the brand oxi-caps.
Digi-Key has them. I have used several thousand of them on some gear that
some users run in hard vacuum, so aluminum electrolytics were out of the
question. I have mis-connected a few of the oxi-caps, and can verify they
will char a bit, but not burst into flame.

Jon

[Ian Field]

"bitrex" <bit...@de.lete.earthlink.net> wrote in message
news:5601ad59$0$5917$4c5e...@frugalusenet.com...

> So I'm working on repairing a Korg MS2000B synthesizer for a friend with a
> dead power supply. Here's the service manual:
>
> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf
>
> The first thing I notice when looking inside is that the small SMT 100uF
> 10V tantalum capacitor C109 has completely vacated - it appears to be
> gone, blown right off the board. There are some little fragments rattling
> around in the case.
>
> I have little experience with tantalum capacitors. Any suggestions for a
> more reliable replacement?
>

You can get MLCC capacitors as big as 180uF - but it won't fit in the
original space.

They're mostly advertised as SMD, but that certainly won't fit - a few
suppliers offer resin dipped leaded versions that you could form the leads
to meet the pads.

Aluminium electrolytics of any kind are a no no! - there was much chatter
about organic semiconductor electrolytics a decade or so ago, that were
claimed to be as good as tantalum, but it lately seems to have gone very
quiet on that front.

Tantalum electrolytics are *VERY* intolerant of reverse voltage, even just a
little bit makes them go leaky. When the normal supply comes back - if it
can shift much current; the tantalum goes off like a match head!

[John Larkin]

On Wed, 30 Sep 2015 19:42:56 +0100, "Ian Field"
<gangprob...@ntlworld.com> wrote:

>
>"bitrex" <bit...@de.lete.earthlink.net> wrote in message
>news:5601ad59$0$5917$4c5e...@frugalusenet.com...
>> So I'm working on repairing a Korg MS2000B synthesizer for a friend with a
>> dead power supply. Here's the service manual:
>>
>> http://www.loscha.com/scans/Korg_MS2000_Service_Manual.pdf
>>
>> The first thing I notice when looking inside is that the small SMT 100uF
>> 10V tantalum capacitor C109 has completely vacated - it appears to be
>> gone, blown right off the board. There are some little fragments rattling
>> around in the case.
>>
>> I have little experience with tantalum capacitors. Any suggestions for a
>> more reliable replacement?
>>
>
>You can get MLCC capacitors as big as 180uF - but it won't fit in the
>original space.
>
>They're mostly advertised as SMD, but that certainly won't fit - a few
>suppliers offer resin dipped leaded versions that you could form the leads
>to meet the pads.
>
>Aluminium electrolytics of any kind are a no no! - there was much chatter
>about organic semiconductor electrolytics a decade or so ago, that were
>claimed to be as good as tantalum, but it lately seems to have gone very
>quiet on that front.

The polymer aluminums are really good. Low leakage, low ESR, don't dry
out.

[Ian Field]

"John Larkin" <jjla...@highlandtechnology.com> wrote in message
news:06do0bta4cb3mng54...@4ax.com...

Saw an article about those a while ago - did they ever take off?

The organic semiconductor variety were supposed to be the "dog's nuts" - but
all the hoo ha seemed to mysteriously fade away.

[Piotr Wyderski]

John Larkin wrote:

> The polymer aluminums are really good. Low leakage, low ESR, don't dry
> out.

Do they exist in the upper mF range (4700+uF) for, say, 35V?

Best regards, Piotr

[John Larkin]

Check the distribs, but I think not. The CV products seem low, like
4700 at 2.5v. Don't know why.

[Phil Hobbs]

Well, in LV SMPSes you really really care about ESR.

[Jon Elson]

John Larkin wrote:


>>Al polys can make voltage regulators oscillate. Tantalums have a nice
>>middle-of-the-road ESR that makes 7800s happy.
>
> My favorite cheap "MDO" regulator, the LM1117, loves a 10 uF tantalum
> on its output.
I've had excellent results using two 22uF aluminum electrolytics, one on the
input, one on the output, of ZLDO1117 regulators. I've built several
hundred devices with that setup, to produce 1.2 to 3.3 V supplies for FPGAs.

Jon

[Jon Elson]

rickman wrote:


>
> Is it about clearing damage or just to show the added resistance
> prevented the failure? I found the story a bit hard to follow.
>
I believe he set up the production line to ramp up the supply voltage with
current limiting on EVERY board as it comes out of the reflow oven.

Jon